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Network Interface Card (NIC) Teaming

Updated: May 9, 2012

Applies To: Windows Server 2012



NIC teaming is a built-in feature of Windows Server 2012, and allows you to provide fault tolerance for your network adapters. NIC teaming allows multiple network interfaces to work together as a team, preventing connectivity loss if one network interface card fails. It allows a server to tolerate network interface card and port failure up to the first switch segment. NIC teaming also allows you to aggregate bandwidth from multiple network adapters, for example, so four 1-gigabit (Gb) network adapters can provide an aggregate of 4 Gb/second of throughput.

The advantages of a built-in teaming solution are that it works with all network interface card vendors, spares you from any potential problems that proprietary solutions cause, and provides a common set of management tools for all adapter types.

You can configure outbound traffic to be distributed among the available network adapters by using modes for network traffic distribution. These modes keep all packets that are associated with a single flow (TCP stream) on a single interface, which minimizes the possibility of out-of-order packet arrival scenarios. The NIC teaming feature uses the following modes for network traffic distribution.

  • Originating media access control (MAC) address mode. In cases where virtual machines (VMs) have independent MAC addresses, you can configure the MAC address of each VM as the basis for dividing network traffic. There is a major advantage in using this mode with virtualization: because the adjacent switch sees specific source MAC addresses on one connected interface, the switch balances the egress load (the network traffic from the switch to the host) on multiple links based on the destination MAC address per VM. This is particularly useful when Virtual Machine Queue (VMQ) is used as a queue and can be placed on a specific network interface card where the traffic is expected to arrive. However, this mode might not be detailed enough to get a well-balanced distribution and will always limit a single VM to the bandwidth available on a single interface.

  • Hashing mode. This mode creates a hash that is based on components of the packet. The mode then assigns packets that have that hash value to one of the available interfaces, which keeps all packets from the same TCP stream on the same interface. Frequently, this mechanism alone is sufficient to create a reasonable balance across the available interfaces. The components that can be used as inputs to the hashing mode include:

    • Source and destination MAC addresses

    • Source and destination IP addresses with or without considering the MAC addresses (2-tuple hash)

    • Source and destination TCP ports, usually used along with the IP addresses (4-tuple hash)

    The 4-tuple hash creates a finer distribution of traffic streams, resulting in smaller streams that can be independently moved between interfaces. This algorithm is not compatible with IPsec; if IPsec is deployed, this algorithm reverts to a 2-tuple hash.

  • Broadcast mode. This mode broadcasts all packets on all interfaces. It does not balance the network traffic load and it causes a need for significant extra processing to drop duplicate packets at the receive side.

In addition, the NIC teaming feature uses the following two sets of configuration modes for use with switches:

  • Switch-independent modes. These modes make it possible for network interface card team members to connect to different switches because the switch does not know that the interface is part of a team at the host. These modes do not require the switch to participate in the teaming.

  • Switch-dependent modes. These modes require the switch to participate in the NIC teaming. Here, all interfaces of the team are connected to the same switch.

Windows Server 2012 allows a virtual machine to have virtual network adapters connected to more than one Hyper-V switch and still have connectivity even if the network interface card under that switch becomes disconnected.

Because failover between network adapters in a virtual machine might result in traffic being sent with the MAC address of another interface, each Hyper-V switch port associated with a virtual machine that is using NIC teaming must be set to allow MAC spoofing. Because some solutions that utilize Single-Root Input/Output Virtualization (SR-IOV) do not support MAC spoofing in the hardware, NIC teaming — and particularly the failover aspects of NIC teaming — might not work when SR-IOV network adapters are present.

Incompatibilities. The NIC teaming feature is compatible with networking capabilities in Windows Server 2012 with three exceptions:

  • SR-IOV

  • Remote Direct Memory Access (RDMA)

  • TCP Chimney

For SR-IOV and RDMA, data is delivered directly to the network interface card without passing it through the networking stack. Therefore, the network interface card team cannot see or redirect the data to another path in the team. In this release, TCP Chimney is not supported with NIC teaming.

For more information about NIC teaming, see NIC Teaming Overview.

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